86 INORGANIC EVOLUTION , [CHAP. 



the triplets in the ordinary line spectrum of a substance may really 

 be remnants of compound flutings, and such inquiries as these really 

 seem to justify that suggestion. 



We arrive at the fact that the term " series " applies to related 

 lines. It is impossible to suppose that these wonderful rhythmic 

 series of lines are not related in some way to each other, and that 

 being so we have to study their wave-lengths, that is, their positions 

 in the case of any one element to find out and define the relationship ; 

 and not only so, but to see if any relation exists between the lines of 

 different elements. 



A Shoi't History. 



The history of this quite modern inquiry is not very long, but 

 short as it is I only propose to refer to it in the briefest possible 

 manner. 



The first attempt to discover relationships among the lines of 

 spectra was made by Lecoq de Boisbaudran,* who investigated the 

 spectrum of nitrogen. The conclusions he arrived at suggested 

 that the luminiferous vibrations of the molecules could be compared 

 with the laws of sound, but as these were not based on wave-length 

 determinations of sufficient accuracy, and also were not confirmed by 

 Thalen, no great weight could be attached to the result. 



Stoney,f who followed up these investigations, was more success- 

 ful ; he showed that the hydrogen lines C, F, and h were connected 

 by the relationship 20 : 27 : 32. 



Several other workers Reynolds, Soret, &c. took the subject up r 

 but it was left for the more thorough work of Schuster J to show that this 

 theory could no longer be considered as expressing the law connecting 

 the mutual relationships between the wave-lengths of lines in a 

 spectrum. 



Liveing and Dewar next called attention to the fact that the 

 distance between two consecutive lines of these groupings decreases 

 with diminishing wave-lengths, so that eventually the lines asymptoti- 

 cally approach a limit. " Harmonic " was the term they used to 

 express such a series of similar groups of lines. 



It was, however, the work of Balmer which gave the subject the 

 mpetus by which it has of late years made great progress. 



Balmer|| published a formula by which the positions of the hydro- 



* Comptes rendus (1869), vol. Ixix, p. 694 



f Phil. Mag. (1871), [4], vol. xli, p. 291. 



J Brit. Assoc. Report, 1880; Proc. Soy. Soc. (1881), vol. xxxi, p. 337. 



Phil. Trans. (1883), p. 213, and previously. 



|| Wied. Ann. (1885), vol. xxv, p. 8. 



